The Method to Measure the Complex Permittivity of Trace Powder with Open-ended Coaxial Probe*

In this paper, a method for the measurement and inversion of the complex permittivity (CP) of trace powder materials (milligrams) within the microwave band. A kind of open-ended coaxial probe (OECP) with short-circuited termination is proposed as the test fixture for the trace powder samples to measure the reflection factor. And the spectral-domain model of the OECP is created to establish the relationship between the CP and the reflection coefficient. Then, the CP can be inversed with the principal mode reflection coefficient. And the OECP was calibrated by three kinds of materials whose CP is known to improve the accuracy of the measurement results. It can be applied to measure the CP of trace powders such as the explosive and flammable materials within the frequency band of 1-20 GHz. Based on the measured CP, the coupling effects of the microwave to these materials can be quantitatively studied, which can be a reference for the safe storage of the explosive and flammable materials.